The isolation of substances from plant and animal sources which effect the growth and differentiation of normal and malignant human cells is paramount in the study of the processes which control cellular activities. By studying these materials as biochemical tools, we may be able to understand the biochemical mechanisms controlling cell proliferation and differentiation. Also, by investigating points where control of metabolic pathways are proliferation. We have established the chemical and biochemical characteristics of the mitogenic and agglutinating components of phytohemagglutin (PHA). The isolectins of PHA show a specificity to different blood cell membranes. The L component has mitogenic activity and agglutinates leukocytes. The E component has less mitogenic activity and agglutinates erythrocytes. The L4 tetramer reversibly inhibits growth of murine leukemia L1210. Rat liver stimulator substance has been partially characterized and studies with respect to the diural rhythm associated with normal rat liver DNA synthesis. BIBLIOGRAPHIC REFERENCES: Egorin, M.J., Felsted, R.L., and Bachur, N.R.: Phytohemagglutinin isolectin stimulation of glucose utilization by lymphocytes. Life Sciences 20: 351-358, 1977. Leavitt, R.D., Felsted, R.L., and Bachur, N.R.: Biological and biochemical properties of Phaseolus vulgaris isolectins. J. Biol. Chem. 252: 2961-2966, 1977.